The Federal Communications Commission has announced that AT&T has agreed to pay $700,000 in order to settle a claim that they moved select customers to a mandatory monthly data plan after promising them they could keep their existing pay-as-you-go plan.

The customers in question were reportedly grandfathered in to the pay-as-you-go program but were forced to move to a monthly data plan not long after the company started requiring that new smartphone subscribers sign up for a monthly flat rate plan. AT&T first started enforcing this rule in November 2009.

The FCC, acting on customer complaints, launched an investigation into the matter last year. They ultimately determined that customers who replaced a phone under warranty or through insurance or those that moved to a new location were automatically switched to the monthly plan.

The money will be deposited to the US Department of Treasury. Furthermore, AT&T will be required to refund excess charges which could be in the range of $25 to $30 for each month affected.

AT&T has also agreed to a compliance plan that includes additional training for customer care reps, new consumer notifications and occasional FCC updates on their progress. The company is responsible for searching through their database to find all customers that were affected and issue refunds accordingly.

It's unclear exactly how many customers were switched to the newer plans. Without this information, it's impossible to gauge with any degree of accuracy just how much this blunder could cost AT&T in addition to the FCC fine.